Physical inactivity is a primary driver of Sri Lanka's growing Non-Communicable Disease (NCD) burden, placing the country among one of the most physically inactive populations in the South-East Asia Region. Despite Sri Lanka's endorsement of the Global Action Plan on Physical Activity (GAPPA) (2018 – 2030) and ongoing Health and Physical Education (HPE) curriculum reforms, no empirical evidence exists on how GAPPA's school-based Physical Education (PE) recommendations are being translated into national curriculum practice. Addressing this gap, this qualitative case study aimed to examine how national policymakers in Sri Lanka's Ministry of Education (MoE) and National Institute of Education (NIE) perceive and navigate this translation process, exploring their awareness of GAPPA, their interpretations of its relevance, and the cultural and contextual factors shaping it. The study combined a content analysis of the existing Grade 10 and Grade 11 national HPE curricula and teachers' guides, assessed against a codebook of 17 sub-codes derived from GAPPA's Action 3.1 school-based PE recommendations, with a thematic analysis of semistructured interviews with eight purposively selected policymakers. Both sets of findings were interpreted through the policy transfer framework of Dolowitz and Marsh (2000) and Kirk's (2010) concept of sportification. The content analysis revealed limited and uneven GAPPA alignment across both curriculum documents, with no sub-code achieving a Fully Present rating. NCD prevention emerged as the strongest area of alignment, while physical literacy, teacher training, active travel, and sedentary behaviour reduction were largely or absent. The thematic analysis identified eight themes, with sport dominance and examoriented culture emerging as the most pervasive constraints, collectively revealing a reform process driven by genuine ambition at the NIE level but undermined by differential GAPPA awareness, limited PE specialist capacity, resource scarcity, sociocultural barriers, and political instability. The integrative analysis characterized Sri Lanka's GAPPA translation as voluntary but selective, incomplete, and structurally constrained, reflecting not a failure of intent, but a failure of conditions. The findings contribute to an emerging evidence base on GAPPA implementation in lower-middle-income country contexts, offering transferable lessons and practical insights for comparable South-East Asian countries facing similar challenges in translating global physical activity policy into national educational practice.